Show HN: I built a small browser engine from scratch in C++

Posted by crediblejhj 9 hours ago

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Hi HN! Korean high school senior here, about to start CS in college.

I built a browser engine from scratch in C++ to understand how browsers work. First time using C++, 8 weeks of development, lots of debugging—but it works!

Features:

- HTML parsing with error correction

- CSS cascade and inheritance

- Block/inline layout engine

- Async image loading + caching

- Link navigation + history

Hardest parts:

- String parsing(html, css)

- Rendering

- Image Caching & Layout Reflowing

What I learned (beyond code):

- Systematic debugging is crucial

- Ship with known bugs rather than chase perfection

- The Power of "Why?"

~3,000 lines of C++17/Qt6. Would love feedback on code architecture and C++ best practices!

GitHub: https://github.com/beginner-jhj/mini_browser

Comments

Comment by _ache_ 1 hour ago

Impressive. Kudos.

You realise that it's only a toy implementation aimed at learning and not a full implementation. The parsing of HTML alone is way more complex than your actual implementation not mentioning at lot of things like the rendering or network (outsourced to Qt).

Still a nice achievement that get you to understand why making a browser is a very complex task.

Comment by vintagedave 4 hours ago

> I had to implement recursion, which I wasn't familiar with.

The amount of learning this person has done is incredible. Kudos.

I also appreciated seeing they used AI and tutorials yet fixed bugs themselves, as a way to demonstrate they understood I the code.

Comment by 3 hours ago

Comment by noo_u 5 hours ago

This is a really awesome project! If you have time/interest, you could try to build a simple http server now, that your browser could communicate with. Then you could try to implement a simple version of TCP/IP, and look into how lower level networking works. Great job!

Comment by zabzonk 5 hours ago

In my experience, not a good idea to write both the client and the server for a given protocol which use each other. Far too easy to misunderstand the protocol. I remember doing this for a training course I wrote for OLE (later COM) years ago. The client and the server worked perfectly together, just not with correctly implemented OLE clients and servers.

Comment by snerbles 3 hours ago

Just slap a new legally-distinct-but-still-confusing name on your client/server pair, and use it as a marketing tool to sucker in purchasing managers.

Like EtherNet/IP, where the IP somehow stands for "Industrial Protocol".

Comment by zabzonk 2 hours ago

Ah, but what if one your clients needs to use, let us say, Excel...

My mistakes with the training course code would have been fixed if the company would have bought Excel licenses fof our customer workstations.

And I just remembered it was DDE (dynamic data exchange), not OLE. OLE was much better specced than DDE. Like I said, it was way back when. But the basic rule (don't test using both a home-grown client and server) still applies.

Comment by rustyhancock 5 hours ago

The real full stack engineering

Comment by ge96 5 hours ago

But did they make their own CPU?

Comment by aruametello 4 hours ago

... did they mine their own minerals?

this could go into a sagan's "If you wish to make an apple pie from scratch, you must first invent the universe."

Comment by Novosell 26 minutes ago

Like any self-respecting baker, I have a cabinet full of universes which produce various pies.

Comment by HPsquared 2 hours ago

And ideally use your own philosophy, concepts and language when engineering everything. No English language, Latin alphabet or Arabic numerals!

Comment by grougnax 4 hours ago

This might be the hardest thing ever in computer science, kudos!

Comment by solusipse 4 hours ago

lol

Comment by butz 4 hours ago

Good job! You should consider contributing to a similar small browser - Dillo @ https://dillo-browser.org/ , and help to build a complete tiny browser.

Comment by robshippr 3 hours ago

Incredible job here. Really took a lot of work to get this done. Keep it up.

Comment by xacky 5 hours ago

I follow a lot of the alternate browser engines and am always looking for new ones outside of the big three. You should use your experience to get a career in the browser tech world as we are dangerously close to the Chromium only web.

Comment by skybrian 4 hours ago

I think this is cool as long as you don't use it to do your banking, and it needs to be running in a VM or on a Raspberry Pi or something. The Internet is dangerous. Something something don't write your own crypto.

Also, there's a big difference between running a handmade browser that I wrote and trusting one that some stranger wrote. I guess I'm going to have to try writing my own someday :-)

Comment by lasgawe 5 hours ago

This is one of the hardest projects of its kind. Congrats! looks cool.

Comment by userbinator 3 hours ago

Interesting to see everyone seemingly writing their own browser lately. Ironic to think that AI assistance, from Google itself, might be what ends up breaking their browser monopoly.

(Speaking as someone who also started writing my own long ago, and it's far from complete.)

Comment by einpoklum 2 hours ago

> everyone seemingly writing their own browser lately

Can you name/link to a few examples? I know about Ladybird:

https://github.com/LadybirdBrowser/ladybird/

but haven't noticed other initiatives.

> might be what ends up breaking their browser monopoly.

This post is a toy project, not a full-fledged browser engine, which is a large beast (even when you _don't_ do everything from scratch)

Comment by 3 hours ago

Comment by Imustaskforhelp 2 hours ago

Indian high school senior here about to start CS in college here.

Your project feels phenomenal. Definitely starred.

I was actually trying to create a browser (in golang) myself as well (using LLM assistance) & I really couldn't do it after countless efforts.

https://github.com/SerJaimeLannister/golang-browser Much of it was just curiosity towards if LLM's could port the rust project by emsh https://emsh.cat/one-human-one-agent-one-browser/ into golang & this has led to some really insightful discussions between me and emsh on bluesky

This is actually really pretty cool as I was targeting a ~10k loc for golang from the ~20k loc of rust (given how golang has networking binaries and other stuff)

I guess this is really cool. I was always really averse to C++ preferring golang. I think I am ken-thompson pilled for the most part lol.

Anyways its really great to see people my age working in similar ideas. Somehow it gives us I guess a more sense of connection like I am not alone doing these things and I guess its pretty cool feeling seeing others do similar stuff and learning from them!

I have starred your repo and good luck for college too man! Hope to communicate with ya.

Edit: Another comment here as someone here mentioned that you used LLM, which LLM did you end up using and how'd you use it. For me personally, the most (success?) that I found which could generate a hackernews without any styles and anything was via their computer-use agent model (which I am thinking of downloading & working with kimi-cli to add more styling and other stuff as well in golang just out of curiosity)

I don't really mind if you used LLM, but I am curious as to how in this instance.

Comment by pipeline_peak 4 hours ago

We need more projects like this.

People making all sorts of libraries for HTML/CSS parsers, render trees, layout models etc.

I don’t want to see a world where everything runs on top of Chromium and we all just unwittingly submit to it.

Comment by luskira 5 hours ago

this is so cool man congrats!

Comment by lifetimerubyist 5 hours ago

Cursor is a 30 billion dollar corporation that couldn’t do this with practically unlimited compute for their AI.

Well done.

Comment by quentindanjou 4 hours ago

How much was coded with an LLM and how much do you understand?

Comment by forgotpwd16 3 hours ago

Excluding recent refactor commits code seems to be handwritten, maybe lightly AI-assisted.

Comment by FEELmyAGI 3 hours ago

Based on what? In fact, the commit messages sure make it seem like someone who only knows how to use git to to take snapshots, exactly like when one turns off their brain and vibe codes, and after chatting enough with the chatbot to get their next feature seemingly to work make some sort of "updated bla" commit with no reference to the extremely detailed code change they just made.

https://github.com/beginner-jhj/mini_browser/commits/main/

Comment by forgotpwd16 1 hour ago

You seem to have gotten used to perfect written commit messages by Claude. Many people, especially those starting out with, or not heavily using, git, do write messages like that. (edit: To be honest sometimes I too make temporary "wtf" commits; I just later squash them and no one knows.) That can actually be seen in this very repo by the refactor ones. And, the commits themselves are actually where I'm basing it. Small changes (vibe coders tend to forget a vcs exists; why we see 20k LOC first commits), commented-out code parts (have you ever seen AI commenting out code?), plain code comments (again compare to what refactor commits introduce).

Comment by 1 hour ago

Comment by quentindanjou 3 hours ago

I am not sure on what you are basing this. Even the post itself looks written by an LLM.

I might be wrong, things are always evolving and it is going to be more and more difficult to spot. But I was genuinely asking OP, and I don't have the intention of undermining their achievement! (it stays cool even with use of LLM)

Comment by olliem36 4 hours ago

Did you use GPT 5.2 Codex? lol

Comment by samiv 5 hours ago

Since when does homework feature on the front page of HN? I find this very odd...

Comment by antirez 5 hours ago

Probably more complex project than projects 99% of what software developers with a real job do daily.

Comment by 5 hours ago

Comment by Imustaskforhelp 2 hours ago

The fact that literally the Creator behind Redis has to go and point this out straight up proves this.

Also Antirez, I am in high school and I can literally write it in writing that there's literally no school with such homework assignments imo. I have written a comment about seeing the curriculum of one of my other friends and my anecdotal evidence talking to friends.

There's literally zero doubt in my mind that there's no such homework assignment.

Comment by dag11 4 hours ago

What high school CS class (or even college class) is assigning a project to implement a minimal web renderer?

This is super impressive.

Comment by Imustaskforhelp 2 hours ago

I am in High school & in my school for some reason CS isn't taught but I still taught one of my friends CS from my tuition you can say.

I looked at his book and wanted to teach him python. You can say its senior high school and what I taught him was what keywords mean in python and operators mean in python etc.

A lot of it was just semantic. Could be the fact that it was first chapter and he came to me when his exam was just some few days later.

I swear but the hardest thing I observed in that book was probably some SQL from what I heard or maybe some minor Java or the fact that it had file access within python or atleast that's what I observed.

The OP's comments are clearly weird and feel like something which should be ignored.

This project is really really cool imo. (Heck I was trying out literally the same thing too but over golang out of curiosity but really didn't land anywhere and the fact that the creator of this was able to still is pretty impressive even if they used LLM or not!, on which I haven't felt any clarification but I just wanted to point how both are really really cool!)

Comment by ikamm 5 hours ago

Nowhere in the post does OP say this is a homework assignment. All they said was that they are a high school senior.

Comment by lotusw0w 4 hours ago

Name one college/university program with homework as impressive as this. This is a serious request

Comment by eichin 2 hours ago

To combine with the "but did he build a cpu" thread, back-in-the-day the term project for MIT 6.004 was "build a CPU with TTL", with a very open-ended "performance race" extra credit project at the end. (At least one of the highest scorers went on build a network performance hardware company and sold it to Broadcom :-)

(If the "build a CPU" part doesn't impress, it was common to build an entire compiler toolchain to go with it; also it was long enough ago that a web browser really was a weekend project :-)